Fuel injection systems more particularly for liquid fuel burners

ABSTRACT

In order to obtain at low fuel-supply rates the benefit of ultrasonic atomisation assistance in the case of a swirl-type atomiser nozzle, the small-diameter horn of an ultrasonic vibrator extends axially through the swirl chamber of a swirl atomiser into close vicinity of the final outlet orifice of the conical end portion of the chamber so that the active tip of the horn can atomise the fuel as the fuel passes through the orifice while the horn is cleared by the hollow core of the swirl when the fuel-supply rate is sufficeint to ensure swirl atomisation. A pressure-sensitive switch then preferably cuts off the energisation of the oscillator for the ultrasonic transducer. A change-over valve controlled by the pressure-sensitive switch may be employed for diverting at low flow rates the fuel flow so that instead of entering the swirl chamber the fuel flows through an axial bore of the atomiser horn.

United States Patent 11 1 Broad et al.

[ F UEL-INJECTION SYSTEMS, MORE PARTICULARLY FOR LIQUID-FUEL BURNERS[75] Inventors: Michael John Broad, Enfield,

Middlesex; Norman Moss, Ilford, Essex, both of England [73] Assignee:Plessey Handel Und Investments A.G., Zug, Switzerland [22] Filed: June21, 197] [21] Appl. No.: 155,092

[ July 17, 1973 752,746 2/1967 Canada 239/102 Primary ExaminerLloyd L.King Attorney-Alex Friedman, Harold 1. Kaplan et al.

[57] ABSTRACT In order to obtain at low fuel-supply rates the benefit ofultrasonic atomisation assistance in the case of a swirl-type atomisernozzle, the small-diameter horn of an ultrasonic vibrator extendsaxially through the swirl chamber of a swirl atomiser into closevicinity of the final outlet orifice of the conical end portion of thechamber so that the active tip of the horn can atomise the fuel as thefuel passes through the orifice while the horn is cleared by the hollowcore of the swirl when the fuel-supply rate is sutficeint to ensureswirl atomisation. A pressure-sensitive switch then preferably cuts offthe energisation of the oscillator for the ultrasonic transducer. Achange-over valve controlled by the pressure-sensitive switch may beemployed for diverting at low flow rates the fuel flow so that insteadof entering the swirl chamber the fuel flows through an axial bore ofthe atomiser horn.

4 Claims, 3 Drawing Figures Patented July 17, l9?3 3346,57

F10. 3 EN FUEL-INJECTION SYSTEMS, MORE PARTICULARLY FOR LIQUID-FUELBURNERS This invention relates to liquid-fuel injection systems, moreparticularly for liquid-fuel burners or gas turbines wherein afuel-injection nozzle dimensioned to ensure adequate pressureatomisation under normal full-load conditions, is formed as part of anultrasonic atomiser so as to permit this ultrasonic atomiser to beoperated to produce high-frequency vibration of the nozzle in thedirection of the nozzle axis to assist atomisation when the rate of fuelsupply is insufficient to produce satisfactory pressure atomisation.

The present invention has for an object to provide an improved system ofthe kind specified in which the fuel-injection nozzle is a so-calledswirl-type atomiser havinga cylindrical swirl chamber into which thefuel from a pressurised supply is admitted tangentially and which at oneend tapers to form a central outlet orifice of smaller diameter.Pressure atomisation is effected in such nozzles by utilisation of therapid swirl movement which occurs when the large-diameter swirling flowproduced in the swirl chamber by the tangential inlets is reduced indiameter to that of the outlet orifice. In order to ensure effectiveatomisation, the rate of fuel admission through the tangential inlets tothe swirl chamber must be sufficient to achieve the necessary high rateof swirl in the outlet, so that at lower rates of fuel consumption andcorrespondingly reduced velocity of the entering fuel, the fuel isliable to leave the nozzle in a so-called tulip formation, rather thanin a spray of fine droplets, and at still lower rates of admission thefuel is liable to leave the nozzle as a more or less axial jet.

According to the present invention 'an ultrasonic vibrator elementhaving a small-diameter horn whose end face has a diameter similar to,or preferably smaller than, the diameter of the outlet orifice, isarranged to extend through the swirl chamber coaxially with the nozzlewith the active tip of the horn arranged in the region of the orifice.Preferably the ultrasonic vibrator is a stepped-diameter amplifier ofwhich the largediameter end is connected to a piezoelectric element orother ultrasonic vibrator, while the reduced-diameter portion or horn ofthe vibrator extends from the opposite surface of the large-diameterportion in the axial direction of the chamber, its active tip beinglocated in the region of the nozzle orifice, while the nodal face of theultrasonic atomiser closes the swirl chamber at its end remote from thenozzle orifice. A further object of the invention is to povide acombined swirl-type and ultrasonic atomizer device in which theultrasonic atomizer means, while effective to ensure atomization atrelatively low rates of liquid supply, at which the atomization achievedby swirl action is insufficient to ensure droplet atomization, willcause minimum interference with the swirl-action atomization at higherrates ofliqid supply at which the atomization by swirl action isadequate without the assistance of ultrasonic vibrations. With thisobject in view the ultrasonic vibrator is so arranged that at high flowrates, when the nozzle operates effectively as a swirl atomiser, theultrasonic vibrator element lies in the hollow core of the circulatingflow so as not to interfere with the swirl action of the latter. Thismakes it possible to cause the ultrasonic vibrator to be de-energised ifdesired, for example by the action ofa pressure switch, when the rate offuel supply is suffieient to maintain effective swirl atomisation, whilewhen the flow rate is lower, the diameter'of the hollow swirl core isalso reduced so that the 'flow will make contact with the end of thevibrator horn, enabling the end of the horn to transmit its ultrasonicvibrations to the fuel passing through the orifice, thus ensuring itsatomisation independently of the. swirl-'atomising action.

By way of a modification, the horn of the ultrasonic vibrator may beprovided with an axial bore leading to an outlet orifice in the activeend face of the horn, and at low rates of fuel supply the fuel is causedto enter this axial bore via a radial passage near the nodal zone of thevibrator. Effective ultrasonic atomisation of the fuel supplied is thusensured without having to reply on a radially inward fuel flow componentin the nozzle of the swirl chamber to place the fuel into contact withthe active tip of the horn.

Two embodiments of the invention will now be described in more detailwith reference to the accompanying drawings, in which FIG. 1 is asomewhat diagrammatic view of a liquidfuel injection system embodyingone form of the invention, the swirl chamber and nozzle being shown inaxial section,

FIG. 2 is a similar view of a modified system, and

FIG. 3 is a fragmentary sectional elevation of the active tip portion ofthe vibrator horn of the embodiment illustrated at FIG. 2.

In the system illustrated by FIG. 1, the swirl atomiser has a bodycontaining a swirl chamber 1 enclosed by a cylindrical circumferentialwall 2, which is joined at the outlet end of the chamber by a conicalwall portion 3 which tapers from the cylindrical wall 2 to asmallerdiameteroutlet orifice having a throat 4. Adjacent to theopposite end of the swirl chamber 1, a number of tangential ports 5 forthe admission of liquid fuel to this chamber extend through the wallportion 2 from a gallery 6 surrounding the ported portion of thecylindrical wall 2, and the chamber 1 is closed at its inlet end, beyondthe ports 5, by the large-diameter portion 7 of a stepped ultrasonicvibrator, which has a small-diameter stem or horn 8 extending axiallythrough the chamber 1. The active tip 9 of this horn is arranged withinthe chamber 1, just short of the outlet orificethroat 4. Attached to theoppositely facing surface of the largediameter portion 7 of the vibratoris a piezoelectric element 10 the opposite side of which is arranged toact on a suitable balance member 11, which is electrically connected toan ultrasonic electric oscillator 12 operating at the resonant frequencyof the vibrator 7, 8. A pump 13 supplies fuel to the gallery 6 via afuel-control valve 14, and the pressure in the line 15 conducting thefuel from the valve 14 to the gallery 6 is communicated to a pressureswitch 16 in power lines 17 adapted to be connected to an electricalpower supply and leading to the oscillator 12.

When fuel is admitted by the valve 14 at low rates of flow, the pressureswitch 16 is closed so that the ultrasonic vibrator is energised at itsresonant frequency with a high-frequency alternating voltag'e. Althoughthe fuel is introduced into the swirl chamber via the tangential inlets5, its energy is insufficient to establish a vortex within the swirlchamber, and the flow is there fore essentially axial. When the fuelreaches the region of the orifice 4, it makes contact with the vibratingtip 9 of the stem or horn 8 of the ultrasonic vibrator, so

that ultrasonic vibration of the vibrator will break-up the fuel intodroplets and cause these to be ejected via the orifice 4. When the flowrate of the fuel into the swirl chamber is increased, the increased fuelpressure will make sufficient energy available to establish somelow-energy vortex in the swirl chamber 1. in the absence of anultrasonic atomiser, such vortex would result in the production ofaso-called tulip-type flow from the orifice 4, a flow which gives onlypoor atomisation. The pressure switch is therefore so constructed thatthe pressure developed in these circumstances is still insufficient toopen the pressure switch 16, so that the piezoelectric element remainsenergised with high-frequency electric power, and as a result thevibrating tip 9 of the vibrator born 8 will add atomising energy to theliquid fuel as it enters the outlet orifice 13, thus causing the tulipto fragment and good atomisation to be ensured.

When the fuel-flow rate, and accordingly the pressure, is still furtherincreased, the energy of the incoming fuel fed through the tangentialports 5 will eventually become sufficient to produce a high-energyvortex within the swirl chamber 1, and the fuel emitted from the orifice4 will in that case be effectively atomised by the swirl action of thefuel so that the operation of the vibrator horn 8 is not required underthese circumstances. At the same time the vortex within the swirlchamber 1 will form a hollow core of sufficient diameter to clear theultrasonic vibrator horn 8, and the high pressure of the fuel in lineoccurring in this case will open the pressure-sensitive switch 16 andthus cut-off the energisation of the oscillator by the electrical supplylines 17.

in the modified embodiment illustrated in FIG. 2 those parts which areidentical with those illustrated in FIG. 1 have been given the samereference numerals, and only the altered parts will be described. Thehorn of the ultrasonic atomiser, which has been given the referencenumber 18, has an axial bore 19 which communicates with a radial bore 20in the large-diameter portion 7 of the atomiser. The fuel-supply line 15coming from the fuel control valve 14, which in FIG. 1 leads direct tothe gallery 6, leads in this embodiment to a change-over valve 21, whichis so controlled by the pressure switch 16 that it willadmit fuel to aline 15a leading to the gallery 6 only when the pressure switch 16 isopen, while when pressure switch 16 is closed, that'is to say at lowfuel pressures, the change-over valve 21 is moved to a position in whichit diverts the flow from line 15 to an alternative line 15b which leadsvia the radial bore 20 to the axial bore 19 of the ultrasonic horn l8.

Under such low-pressure conditions accordingly all the fuel is suppliedthrough the axial bore 19 to thc active tip 22 of the horn 18 so that inthis case all the fuel is subjected to the action of the ultrasonicvibrations of the horn. Preferably the outlet of the axial bore 19" atthe active tip of the atomiser horn 18 is formed as a sharp-edgedorifice 22 as shown in the larger-scale sectional elevation of FIG. 3. iT

What we claim is:

1. An atomizing device for liquid fuel an'dother liquids, whichcomprises: a body containing a swirl chamber of circular cross-section,a liquid-inlet passage lead ing tangentially into said chamber, and anozzle outlet that extends axially from said chamber and has a throatwhose diamter is smaller than that of the swirl cham ber; means forsupplying liquid to said inlet passage at a rate which is variablebetween an upper range in which the energy of the liquid enteringthe-chamber through said inlet passage is sufficient to form in saidchamber a vortex that produces at the nozzle exit effective swirlatomization of the liquid leaving the chamber through the nozzle and hasaninternal cavity of predetermined minimum dimensions," and a lowerrange in which the energy of the liquid entering the swirl sham-t ber isinsufficient to form such atomization producing such vortex, anultrasonic vibrator having a stem terminating in a tip, the vibratorbeing so connected to said body that said stem extends in the swirlchamberalong the axis thereof, the tip of the stem body located withinthe internal cavity of the vortex formed when the rate of liquid supplyis in said upperrange, said tip being located approximately in the planeof the said throat, and the vibrator being operative when energised tovibrate the said tip in the longitudinal direction of the stem.

2. A device as claimed in claim 1, wherein the vibrator stem terminatesshort of the throat of -the nozzle outlet.

3. A device as claimed in claim 1, which includes a pressure-responsiveswitch subject to the pressure of the liquid supplied to said inletpassage and operative to cut-off energisation of the vibrator when thesaid pressure is sufficient to supply liquid at a rate'within said upperrange.

4. A device as claimed in claim 1 wherein the vibrator stem has alongitudinal bore leading to an orifice at the tip of the stem, andwherein the device. includes a pressure-responsive change-over switchsubject to the pressure of the liquid supplied by said liquid-supplyingmeans and operative to divert the liquid supplied so as to admit it tosaid bore instead of admitting it to the swirl chamber when the saidpressure is insufficient to supply liquid to said chamber at a ratewithin said upper range.

1. An atomizing device for liquid fuel and other liquids, whichcomprises: a body containing a swirl chamber of circular crosssection, aliquid-inlet passage leading tangentially into said chamber, and anozzle outlet that extends axially from said chamber and has a throatwhose diaMter is smaller than that of the swirl chamber; means forsupplying liquid to said inlet passage at a rate which is variablebetween an upper range in which the energy of the liquid entering thechamber through said inlet passage is sufficient to form in said chambera vortex that produces at the nozzle exit effective swirl atomization ofthe liquid leaving the chamber through the nozzle and has an internalcavity of predetermined minimum dimensions, and a lower range in whichthe energy of the liquid entering the swirl chamber is insufficient toform such atomization producing such vortex, an ultrasonic vibratorhaving a stem terminating in a tip, the vibrator being so connected tosaid body that said stem extends in the swirl chamber along the axisthereof, the tip of the stem body located within the internal cavity ofthe vortex formed when the rate of liquid supply is in said upper range,said tip being located approximately in the plane of the said throat,and the vibrator being operative when energised to vibrate the said tipin the longitudinal direction of the stem.
 2. A device as claimed inclaim 1, wherein the vibrator stem terminates short of the throat of thenozzle outlet.
 3. A device as claimed in claim 1, which includes apressure-responsive switch subject to the pressure of the liquidsupplied to said inlet passage and operative to cut-off energisation ofthe vibrator when the said pressure is sufficient to supply liquid at arate within said upper range.
 4. A device as claimed in claim 1 whereinthe vibrator stem has a longitudinal bore leading to an orifice at thetip of the stem, and wherein the device includes a pressure-responsivechange-over switch subject to the pressure of the liquid supplied bysaid liquid-supplying means and operative to divert the liquid suppliedso as to admit it to said bore instead of admitting it to the swirlchamber when the said pressure is insufficient to supply liquid to saidchamber at a rate within said upper range.